The delivery of therapeutic substances to mucosal surfaces has inherent difficulties due to the moist surface. This is particularly true for the mucosal surface of the eye where the washing action of the tear film removes much of the therapeutic substance. Estimates of the portion of a drug delivered by means of a topical drop range from 1 to 10% of the drug content. The remaining portion of the drug which does not penetrate or adhere to the eye is removed by tears through the lacrimal ducts where systemic absorption occurs through contact with nasal and gastro-intestinal surfaces.
A common ophthalmic problem, particularly with older people, is the condition commonly known as "dry eye" or dyslacrima. As people age, the tear ducts in the eye produce less moisture. Consequently, the eye becomes dry, inflamed and irritated.
There is a need for a method for treating mucosal surfaces such as, for example, the eye, in order to retain an active agent for a longer period of time.